The specific aim of this proposal is to elucidate the brain stem neuronal mechanisms responsible for the production and coordination of spontaneously occurring and cortically induced rhythmical jaw movements (RJM) resembling mastication in the guinea pig. We propose to systematically search the brain stem reticular formation for neuronal sites which participate in the production of RJMs. This proposal is divided into three main sections. Part one will utilize brain stem microstimulation techniques and field potential analysis within specific motoneuronal pools of the trigeminal motor nucleus to determine if a particular brain stem site has an effect on the motor pool. Part two will involve extracellular recording from reticular neurons of the brain stem during RJMs. Computer analysis and spike triggered averaging techniques will be employed to determine the functional connectivity that exists between the brain stem neuron, motoneuron and masticatory area of the cortex. Finally, intracellular recording from specific identified trigeminal motoneurons innervating the muscles which control opening, closing and lateral movements of the mandible will be obtained during microstimulation of brain stem sites shown to effect the trigeminal motor nucleus. This will allow us to determine the precise synaptic effect these areas exert on the specific motoneurons. The long term goal of the research is to understand how the central nervous system initiates, coordinates, and executes the rhythmical stereotypic movements of the mandible during mastication. Involuntary, rhythmical movements of the jaws occurs in humans during sleep (bruxism). These patients tend to develop myofacial pain. Uncontrolled rhythmical movements of oral-facial structures also occurs during long term administration and withdrawal from anti-psycotic drugs (tardive dyskinesia). The etiology of these movement disorders is unknown. The results of these studies will shed light on the neuronal mechanism(s) responsible for these involuntary rhythmical jaw movements.